The present invention is concerned with improved instrument lighting systems, and is particularly concerned with the provision of indicator dial systems or displays for instruments employing light emitting diodes for illumination.
Incandescent lamps are usually employed to illuminate cockpit instrument displays, but these lamps generate a considerable amount of heat. This heat has often contributed to the premature failure of internal electronic components used in standard displays. In addition, incandescent lamps consume a great deal of power and are easily damaged by shock and vibration. Accordingly, a more effective, more reliable means of illumination is needed to solve the above problem, particularly in conjunction with an instrument dial display system which provides a high contrast ratio between the dial indicia and dial face background, and which causes the lighted dial indicia and pointer to exhibit a specified brilliance or lighted color presentation.
U.S. Pat. No. 3,732,560 discloses a rotatable drum indicator which uses light emitting diode back lighting, with the drum being molded from suitable near-transparent or highly translucent plastic material. However, present dial and light-plate designs do not permit a satisfactory lighted display with light emitting diodes in that the white paint or white colored areas in the presently employed silk screen types of dial designs absorb or attenuate too much light and fail to provide a satisfactory lighting presentation with newly developed light sources, particularly light emitting diodes, and such light sources have a much lower intensity than incandescent lamps.
U.S. Pat. No. 3,503,365 discloses translucent instrument dial means which comprises a three disk assembly including a front disk which can be formed of a plastic film, preferably a black tinted plastic overlay material such as the material marketed as "Lexan" or a photographic negative which has been exposed to light and developed, a center transparent disk and a rear translucent disk. The indicia on the exposed film is formed of an opaque light colored material such as white ink or paint. The patent discloses a light source that is enclosed within a light diffuser and is directed towards the three disk assembly.
U.S. Pat. Nos. 2,395,718 and 2,427,896 disclose instrument display systems making use of "Polaroid" or light-polarizing characteristics.
Other patents disclosing prior art instrument display systems include U.S. Pat. Nos. 2,518,726; 2,824,399; 2,663,107; 2,637,296; and 2,824,954.
Accordingly, one object of the invention is the provision of improved presentations of instrument dial displays, particularly for aircraft instruments. A further object is the employment of light emitting diodes effectively as a source of light in lighting display systems for aircraft, to provide lighted presentations which exhibit a high illumination level and which offer the advantages of long life, lower power consumption and absence of internal heating. A particularly important object is the provision of transilluminated dial presentations for instruments, particularly aircraft instruments, utilizing light emitting diodes as a light source, in combination with a novel instrument dial display, and presentation system, which offers the above noted advantages of the use of light emitting diodes while at the same time providing dial displays which satisfy commercial and military color and/or brightness requirements and which exhibit a uniform color and brightness presentation ranging from maximum illumination to brightness levels near extinction.